The present invention relates to a calibration system of an array antenna receiving apparatus. More particularly, the present invention relates to a calibration system for correcting the change in phase (delay) and amplitude information between antenna radio receiving units in an array antenna receiving apparatus for adaptive antenna control.
Conventional cellular mobile communication systems require the high speed and the high quality of signals and the increase in subscriber capacity. For example, a method for reducing reception gain against the interference from another user and the interference due to delay waves is examined by using an array antenna receiving apparatus comprising a plurality of antenna devices having the high correlation. As a result, a reception directive pattern is formed so that the reception gain is increased in the incoming direction of a desired signal.
The array antenna receiving apparatus comprises the plurality of antenna radio receiving units. In general, in the above-mentioned array antenna receiving apparatus, the amplitudes and phases in the antenna radio receiving units connected to the antenna devices are individually varied every moment. The formatting of the reception directive pattern requires the correction of the variation of the amplitudes and phases. The above operation is called calibration.
For example, Japanese Unexamined Patent Publication (JP-A) No. 11-46180 discloses a conventional calibration system of the above-mentioned array antenna receiving apparatus. Japanese Unexamined Patent Publication No. 11-46180 prepares a technology in which a well-known signal is inputted to antenna radio receiving units connected to antenna devices and a result of demodulating a calibration signal is used. In this preparation, the change in phases (delays) and amplitudes of the antenna radio receiving units, as the demodulating results, which are individually varied every moment, are corrected.
FIG. 1 is a block diagram showing a calibration system of a conventional array antenna receiving apparatus.
The array antenna receiving apparatus comprises an array antenna 1001, multiplexing circuits 1003-1 to 1003-N corresponding to N antenna devices 1002-1 to 1002-N, antenna radio receiving units 1004-1 to 1004-N corresponding to the N antenna devices 1002-1 to 1002-N, user signal processing units 1005-1 to 1005-M corresponding to M users, a calibration signal transmitting unit 1010, and a calibration signal processing unit 1011.
The array antenna 1001 comprises N antenna devices 1002-1 to 1002-N. The N antenna devices 1002-1 to 1002-N are closely arranged so that reception signals from the antenna devices have a correlation, and receive signal obtained by multiplexing a desired signal and a plurality of interference signals.
One multiplexing circuit 1003-i in the N multiplexing circuits multiplexes a calibration signal as an output from the calibration signal transmitting unit 1010 and a reception signal as an output from the antenna device 1002-i. The multiplexing circuit 1003-i multiplexes an input signal at a radio band and outputs the multiplexing signal to the antenna radio receiving unit 1004-i. A multiplexing method is not particularly limited and a code multiplex is used as an example.
The antenna radio receiving unit 1004-i comprises devices such as a low-noise amplifier, a band limiting filter, a mixer, a local transmitter, an AGC (Auto Gain Controller), an orthogonal detector, a low-pass filter, and an analog/digital converter (ADC). The antenna radio receiving unit 1004-i subjects the signal inputted from the multiplexing circuit 1003-i to amplification, frequency conversion from the radio band to a base band, orthogonal detection, analog/digital conversion, and so on. The antenna radio receiving unit 1004-i further outputs the processed signal to the user signal processing unit 1005-i and the calibration signal processing unit 1011. Normally, an AGC amplifier is used for keeping of a power level of the output signal constant independently of the power level of the input signal every antenna radio receiving unit.
The calibration signal processing unit 1011 receives signals from the antenna radio receiving units 1004-1 to 1004-N, extracts the calibration signal from the signals, detects phase/amplitude information of the antenna radio receiving units 1004-1 to 1004-N, and outputs the detected information to the user signal processing units 1005-1 to 1005-M. Herein, the calibration signal multiplexed to the input signal can be extracted.
A user signal processing unit 1005-j corresponding to a user j inputs outputs from the antenna radio receiving units 1004-1 to 1004-N and the phase/amplitude information of the antenna radio receiving units 1004-1 to 1004-N as outputs from the calibration signal processing unit 1011. The user signal processing unit 1005-j corrects the inputs from the antenna radio receiving units 1004-1 to 1004-N by using the phase/amplitude information of the antenna radio receiving units 1004-1 to 1004-N as the outputs from the calibration signal transmitting unit 1010, and increases the reception gain against the incoming direction of the signal to the target user j. On the other hand, the user signal processing unit 1005-j forms a reception directive pattern so that the reception gain is reduced against the interference from another user and the interference due to the delay waves, and outputs a user demodulating signal j which is received by the reception directive pattern.
The calibration signal transmitting unit 1010 generates a calibration signal at the base band and subjects the generated signal to digital/analog conversion and frequency conversion from the base band to the radio band. Thereafter, the calibration signal transmitting unit 1010 forms the calibration signal having the same frequency band as that of reception signals of the antenna devices 1002-1 to 1002-N, and outputs the formed signal to the multiplexing circuits 1003-1 to 1003-N at arbitrary power levels. In this case, the calibration signal processing unit 1011 detects the phase/amplitude information of the antenna radio receiving units 1004-1 to 1004-N every reception power by changing the calibration signals to have a plurality of power levels.
The signals received by each of the N antenna devices 1002-1 to 1002-N include a users desired signal component, an interference signal component, and thermal noise. Further, the desired signal component and the interference signal component include multi-path components, respectively. Generally, the signal components comes in different directions.
The conventional array antenna receiving apparatus shown in FIG. 1 identifies the signal components in different incoming directions and forms the reception directive pattern by using the phase/amplitude information of the signals received by the N antenna devices 1002-1 to 1002-N.
In this case, the antenna radio receiving units 1004-1 to 1004-N generate the change in phase/amplitude therein. Then, information different from the phase/amplitude information of the signals received by each of the original antenna devices 1002-1 to 1002-N is given to the user signal processing units 1005-1 to 1005-M. Thus, the signal components are not accurately identified and an ideal reception directive pattern is not formed.
The calibration signals having the same frequency band as those of the reception signals from the antenna devices 1002-1 to 1002-N are multiplexed thereto. The calibration signal processing unit 1011 detects the phaselamplitude information of the calibration signals extracted from the outputs from the antenna radio receiving units 1004-1 to 1004-N, thereby correcting the phase/amplitude information given to the user signal processing units 1005-1 to 1005-M.
The multiplex of the calibration signals enables the calibration upon operating the array antenna receiving apparatus. That is, the calibration signal is multiplexed to the reception signal and only the calibration signal component can be extracted. For example, code multiplex is used.
A non-linear circuit included in the antenna radio receiving units 1004-1 to 1004-N, in particular, the AGC has the change in phase/amplitude varied depending on the reception power level. Therefore, the calibration signal processing unit 1011 extracts the calibration signals of the outputs from the antenna radio receiving units 1004-1 to 1004-N and detects the phase/amplitude information while changing the power levels of the calibration signals outputted by a power level varying circuit of the calibration signal transmitting unit 1010. Thus, the amount of correction applied to the phase/amplitude information given to the user signal processing units 1005-1 to 1005-M is determined every power level of the calibration signal.
The array antenna receiving apparatus having the above-mentioned calibration means can correct the phase/amplitude information given to the user signal processing units 1005-1 to 1005-M if the change in phase/amplitude is caused in the antenna radio receiving units 1004-1 to 1004-N upon operating the array antenna receiving apparatus. Further, the calibration with high accuracy can be performed corresponding to the power levels of the reception signals.
Consequently, the conventional array antenna receiving apparatus shown in FIG. 1 accurately identifies the signal components varied depending on the incoming directions by using the phase/amplitude information of the reception signals of the N antenna devices 1002-1 to 1002-N, and forms the ideal reception directive pattern.
However, the calibration system of the conventional array antenna receiving apparatus is not suitable to the array antenna receiving apparatus upon operation because it has the following problems.
First, the reception sensitivity of the array antenna receiving apparatus excessively deteriorates in case that the calibration signals are changed at a plurality of power levels upon operating the array antenna receiving apparatus. Further, the phase/amplitude information of the antenna radio receiving units is detected every reception power, thereby performing the calibration. Because the calibration signal is entirely the interference wave for the desired wave as a user signal inputted from the antenna from a mobile machine and, in particular, if the calibration signal with a high level is inputted, the interference signal component is increased. Secondarily, the calibration reduces the number of users of the system. Because the calibration signal becomes the interference wave and the ratio of the user signal from the mobile machine to the interference signal deteriorates, and a transmission output of the mobile machine is increased to demodulate the signal to have a desired signal quality in a base station apparatus.
Accordingly, the present invention is devised to solve the above-mentioned problems and it is an object of the present invention to provide the following calibration system. First, the sensitivity deterioration due to the calibration signal is prevented in the array antenna receiving apparatus upon operation and, further, the calibration with high accuracy can be performed irrespective of a simple structure. Secondarily, there is almost no reduction of the number of users of the cellular system.
A calibration system of an array antenna receiving apparatus according to the present invention relates to a calibration system of an array antenna receiving apparatus for inputting a multiplexing signal which is obtained by multiplexing a well-known calibration signal to signals received from antenna devices forming an array antenna corresponding to the antenna devices, for detecting phase/amplitude information of the calibration signal every antenna radio receiving unit connected to each antenna device, based on the calibration signal extracted from the multiplexing signals, and for correcting a user signal to a mobile machine which is received every antenna radio receiving unit connected to each antenna device based on the phase/amplitude information. For extracting the calibration signal and assuring the ratio between the calibration signal to be need for calibration and the interference signal, the
Calibration system of the array antenna apparatus is characterized by comprising radio control means for detecting a detection voltage of the total reception power of the inputted multiplexing signal, for gain controlling the received multiplexing signal in accordance with the detection voltage, and for outputting the signal controlled, and signal processing means for receiving the detection voltage of the total reception power from the control means, for determining an adaptive calibration time every antenna device based on the detection voltage, and for detecting the phase/amplitude information of the calibration signal from the multiplexing signal based on the longest calibration time among the calibration times.
Specifically, the calibration system of the array antenna receiving apparatus comprises a calibration radio transmitting unit for transmitting a well-known calibration signal, an antenna radio receiving unit connected to corresponding antenna devices forming an array antenna, for inputting a signal multiplexing the calibration signal to a signal received from each antenna device, a calibration signal processing unit for detecting phase/amplitude information of the calibration signal every antenna radio receiving unit based on the calibration signal extracted from each of the antenna radio receiving units, and a user signal processing unit for correcting a multiplexing signal, which is received by each of the antenna radio receiving units based on the phase/amplitude information every antenna detected by the calibration signal processing unit.
The calibration system of the array antenna receiving apparatus further comprises a radio control unit arranged to each of the antenna radio receiving units, for outputting an AGC control signal for controlling gain in accordance with a detection voltage of the total reception power inputted to the corresponding antenna radio receiving unit, and a calibration time determining unit for determining and outputting an adaptive calibration time every antenna radio receiving unit based on the detection voltage of the total reception power inputted to each of the antenna radio receiving units. Therefore, each of the antenna radio receiving units detects the detection voltage of the total reception power of the inputted multiplexing signal, outputs the detection voltage to the radio control unit, and outputs gain of the received multiplexing signal by gain in accordance with the AGC control signal received from the corresponding radio control unit. And the calibration signal processing unit detects and outputs the phase/amplitude information of the calibration signal from the multiplexing signal outputted from each of the antenna radio receiving units based on the longest calibration time among the calibration times of the antenna radio receiving units outputted from the calibration time determining unit.
The calibration signal transmitted by the calibration radio transmitting unit is sent by fixed power which is sufficiently lower than thermal noise power in the array antenna receiving apparatus. The multiplexing signals outputted from the antenna radio receiving units are added by using the common mode by the longest calibration time and the calibration signals included in the multiplexing signals are averaged. Thus, the phase/amplitude information of the calibration signal is detected every antenna radio receiving unit. That is, the phaselamplitude information of the calibration signal by varying the calibration period using the calibration signal having the fixed low power which does not cause the deterioration of the sensitivity.
With the above-mentioned structure, the sensitivity deterioration due to the calibration signal can be prevented. The reduction of the number of users in the cellular system can further be prevented. Moreover, the phase/amplitude information can accurately be corrected with simple structure.
The calibration signal transmitted from the calibration radio transmitting unit may be sent by the fixed power which is sufficiently lower than thermal noise power in the array antenna receiving apparatus. When the calibration signal processing unit detects the phase/amplitude information, the multiplexing signals outputted from the antenna radio receiving units are added by using the common mode by the longest calibration time and the calibration signals included in the multiplexing signals are averaged. Thus, the phase/amplitude information of the calibration signal may be detected every antenna radio receiving unit. Further, the phase/amplitude information of each antenna radio receiving unit may be detected every calibration period having a period length of the longest calibration time.
The calibration time determining unit may determine and output the adaptive calibration time every antenna radio receiving unit based on the AGC control signal from each of the radio control units, in place of the detection voltage of the total reception power.